E-150 5.8 LITER DIES AFTER HOT ON HO

94 E-150, 5.8 ltr V8, only on 90 degree+ days - dies after allowed to idle for any length of time. OK at highway speeds, maybe a little sluggish. If allowed to idle for any lenth of time (exceeding like 3 minutes), results in complete loss of power and dies (occasionally backfires while pedaling). Feathering the pedal will not keep it running. If the car is allowed to cool completely, it runs fine again.
Possibly related: pulled a moderate load around the block with the doghouse off and exhaust headers begin to glow red. Is this normal?
Possibly related: engine 'hunts' for idle during moderate decel. Idles fine at rest, only during decel from highway speeds. Like it is surging until it reaches lower speed at decel. TPS has been changed by dealership. Does this sound like clogged/failed cat converter? Logic is that while I am moving the cat is staying cool enough; when we stop to idle the temp goes up. When the cat is allowed to cool completely the van runs fine again. How to confirm, short of replacement? Could I cool it with a garden hose?

The exhaust glowing red hot is constant with a cat problem, but something else is causing the cat to over heat like that, in the past I have found that a over rich mixture can cause this, something like a faulty fuel injector an be at fault, I would also run a scan to check for any unresolved fault codes, and an exhaust emission test to see how rich or other wise the exhaust is, start here.